New neuromodulation approach shows promise in treating psychiatric disorders
Key Takeaways
Low intensity focused ultrasound (LIFU) directly affects neuronal activity with a high degree of precision.
The biomechanical mechanisms of action are not exactly understood, but LIFU may act in several ways to produce neuronal changes.
Safety guidelines for LIFU have not yet been established, and physicians should adhere to current FDA ultrasound guidelines as minimum safety standards.
The neurocircuitry of underlying psychiatric disorders has been the subject of intense study, especially in cases of treatment-resistant issues such as depression or obsessive-compulsive disorder.[]
Two modalities—transcranial magnetic stimulation (TMS) and transcranial electrical stimulation—are currently the most widely used treatments, but both lack a high degree of spatial focality. Other stimulation methods, such as deep brain stimulation, offer spatial precision but are invasive and therefore riskier.
An emerging technology known as low intensity focused ultrasound (LIFU) shows promise as a new method of brain stimulation. Unlike previous technologies, LIFU directly affects neuronal activity with high spatial precision.
This new treatment technique can be used in superficial and deeper brain structures, and the results of treatment typically last longer.
Low-intensity ultrasound to modulate neuronal activity
At its simplest, ultrasound can be defined as an acoustic, or sound, wave occurring at frequencies undetectable to the human ear. Generally, these frequencies are greater than 20kHz.
At high intensity, ultrasound waves produce enough thermal energy to cause irreversible effects on proteins in brain tissue.[] However, higher frequencies do not penetrate brain tissue as deeply even though they do have better spatial resolution.
Low intensity ultrasound uses ultrasonic intensity that matches or is less than that used in various diagnostic ultrasound applications.[]
In contrast to high intensity ultrasound, LIFU can reliably modulate specific regions of the brain—but this modulation is reversible.
While the exact biophysical mechanisms impacted by and resulting from LIFU are unknown, researchers speculate that the heat produced from the absorption of acoustic energy may actually inhibit neuronal activity.
It is also possible that ultrasound may alter the state of mechanosensitive ion channels by causing conformational changes which induce the same channels to open. These changes may lead to fluctuations in ion levels, ultimately generating action potentials.
Another proposed mechanism of neuromodulation involves acoustic cavitation within the brain’s bilayer membrane, which results in the temporary enhancement of blood-brain barrier permeability.
Researchers hypothesize that bubble cavitation leads to oscillation, which causes the activation of mechanosensitive proteins and may affect membrane permeability.
LIFU safety considerations
Preliminary studies have not shown any brain injury or other serious adverse effects. However, biological effects resulting from ultrasound are still possible. Depending on the exposure parameters, coagulative necrosis may lead to irreversible cell death, although this has only been demonstrated using high intensity ultrasound.
Currently, the U.S. Food and Drug Administration and other regulatory authorities require practitioners to adhere to safety guidelines for diagnostic ultrasound examinations. While not directly applicable to LIFU, these guidelines should be treated as the minimum safety standards during ultrasonic neuromodulation procedures.
Even though LIFU is not currently being used for the treatment of psychiatric disorders, the technology is promising, especially since the effects of the treatment are reversible.
This new approach to treatment may eventually help many patients achieve manageable symptoms or even symptom remission without certain limitations associated with standard brain stimulation treatments.
What this means for you
While LIFU is not used to treat psychiatric disorders at this time, research suggests this new treatment modality has the potential to be a unique treatment tool in addition to standard brain stimulation therapies. It is possible that, at some point in the future, LIFU will become a cornerstone of therapy that is lower cost, more precise, and noninvasive.